Stabilized polyolefin polymer compositions



United States Patent 3,245,9 4? STABELHZED POLYOLEFHN PGLYMER COMPOSETIONS Stanley A. Murdock, 5858 fine Hollow Road,

Concord, Calif. I No Drawing. Filed Jan. 7, 1963, Ser. No. 249,575 19 Claims. (Ci. 260-4585) The present invention relates to the stabilization of olefin polymer compositions against heat and oxidative deterioration by incorporating therein a small amount of a certain phosphorous-containing polyphenolic compound or polymer in combination with dilaurylthiodipropionate or distearylthiodipropionate, which combination is capable of efiiciently stabilizing the polymer and simultaneously capable of withstanding rather severe polymer processing conditions.

Several compounds, including certain phenolic compounds, have been found to be of value for stabilizing polyolefins such as polypropylene and copolymers of propylene with other olefins against discoloration, degradation, and embrittlement. For the most part, the stabilizer has been added to the olefin polymer while it is in molten form. The primary attendant problem of this method of incorporating the chosen stabilizer is that the molten polymer or melt is usually of high viscosity and uniform mixing is not easily nor always attained. In some instances the polymer is first obtained in solid form and must then be heated to a molten state to incorporate the stabilizer.

When solution polymerization of the olefin monomer is employed, one of the last processing steps is the recovery of the polymer in molten condition by evaporation of the solvent. Conveniently, the addition of the stabilizer is at this final stage while the polymer is in the molten state. However, as indicated, obtaining a uniform distribution of stabilizer throughout the polymer composition is not without difficulty, and furthermore, the energy requirements for the mixing are considerable.

It has now been found that it is entirely operable to incorporate the stabilizer in the solution of polymer in solvent prior to evaporation, devolatilizing or otherwise removal of the solvent from the polymer. An excellent homogeneous blend of polymer and stabilizer is thus obtained, and blending with a high viscosity system is obviated. Unfortunately, the conventional stabilizers suited to the purpose of stabilizing such polymers are partially and sometimes essentially completely removed during the solvent removal step. For instance, one method used to remove the solvent is to pass the solution through a series of shell and tube devolatilizers which operate at temperatures in the range of ZOO-300 C. at 1 mm. mercury vacuum. Frequently the solution will be under these conditions for 8-10 hours. Under these severe conditions the stabilizer tends to be carried off with the solvent, or, as frequently happens, the stabilizer begins to break down or decompose. It has been found presently to be of additional advantage to incorporate a suitable stabilizer system in the polymer prior to devolatilization in that it provides an efiicient means for closely controlling the molecular weight of the resulting polymer.

Accordingly, it is the chief concern and primary object of the present invention to provide highly effective stabilizers for olefin polymer compositions which will remain in and be compatible with the polymer compositions under conditions of high temperature and high vacuum.

It is a further object of the invention to provide stabilized olefin polymer compositions.

It is still further object of the invention to provide a means for efliciently and uniformly incorporating highly effective stabilizers into an olefin polymer composition.

These as well as other objects and the attendant benefits and advantages are accomplished in accordance with the present invention which comprises incorporating in a 2 to about 8 carbon-atom aliphatic olefin polymer from about 0.05 to about 0.5 weight percent, based on olefin polymer weight, of a certain variety of a phosphorouscontaining polyphenolic compound or polymer, as hereinafter more fully delineated, and from about 0.1 to about 0.5 weight percent of dilaurylthiodipropionate (DLTDP) or distearylthiodipropionate (DSTDP), based on olefin polymer weight.

While each of the phosphorous-containing polyphenolic compound and the DLTDP or DSTDP individually may have stabilizing effects on the olefin polymer, surprisingly superior and far more desirable results are obtained when a combination of the phosphorous-containin g polyphenolic compound with either or both of the DLTDP or DSTDP is employed. Thus, one aspect of the present invention is the finding that the polyphenolic compound and the DLTDP or DSTDP when used in combination apparently exert a synergistic effect regards their ability to eificiently stabilize the olefin polymer.

The phosphorous-containing polyphenolic stabilizers are remarkably compatible with the olefin polymer compositions and once incorporated therein remain in a generally permanent manner throughout normal usages and exposure as well as rather severe usages, exposure and processing treatments. The olefin polymer compositions containing the stabilizers are excellently enhanced with resistance to becoming discolored and embrittled by heat and oxidative deterioration. The stabilized polymer compositions can withstand, to an unusual degree, lengthy exposure to elevated temperatures in the presence of air without showing any degradive efiects. This, obviously, greatly broadens and extends this field of application and utility of these polymer compositions.

The phosphorous-containing polyphenolic stabilizers are, for the most part, solids at room temperature and may be incorporated in a polymer melt in the conventional fashion by blending the stabilizer in finely divided form with the melt, or by first blending the stabilizer with a small portion of the melt prior to blending that with the main batch.

As indicated, the stabilizers employed in the present invention are advantageously adapted to be added to a solution of the polymer whereby the stabilizer becomes incorporated in the polymer upon removal of the solvent. With this technique, beneficially, the stabilizer is first dissolved or dispersed in a solvent, preferably the same solvent as that in which the polymer is dissolved, and then the stabilizer solution is added to the polymer solution. Although it is possible to add the stabilizer at any solution concentration, profitably, the stabilizer solution is admixed with the polymer solution at the most dilute stage of the polymer solution processing to facilitate mixing and to promote uniform stabilizer distribution.

The phosphorous-conta ning polyphenolic stabilizers that are so advantageously employed in the olefin polymer compositions in the practice of the present invention may be cursorily defined as substances that consist of the condensation products of such aromatic nuclei as hydroquinone, Bisphenol-A (p,p-iso-propylidene diphenol) and related bisphenols, such as the bisphenol sulfones (p,p-sulfonyldiphenol) or biphenol sulfoxides (p,p-sulfinyldiphenol), with phosphorous oxyhalides, such as phosphorous oxychloride and equivalent oxyhalides including the oxybromide; and the partial hydrolysis products of the above indicated condensation products. More specifically, the phosphorous containing polyphenolic polymers that may the employed as stabilizers in the practice of the 3 present invention may be represented by the general structure:

wherein Ar is a difunctional aromatic nucleus selected from the group of those derived from hydroquinone, Bisphenol-A, bisphenol sulfone, bisphenol sulfoxide, and mixtures thereof; each R is independently selected from the group consisting of p,p'-hydroxy phenyl radicals, hydrogen or .an alkali metal, such as sodium, and in which any combination or mixture of the several substituents represented by R may be present in the compound; and n is a number having an average value of at least one and which may be as high as 15 or more.

Even more specifically, a representative structure of a phosphorouscontaining polyphenolic stabilizer-s in general accordance with the Formula I that is derived from hydroquinone may be depicted by the following:

wherein n and R have the same meaning as above. Preferably the molar ratio of difunctional phenol (aromatic nuclei) to phosphorous in the phosphorous-containing polyphenolic polymers is about 5 to 2, respectively, although ratios from about 3 :1 to 1:1 of difunctional phenol to phosphorous, respectively, are genenally quite suitable in the stabilizers.

The phosphorous-containing polyphenolic stabilizers that are utilized are preferably soluble in the common olefin polymer solvents. Thus, the maximum operable molecular weight of the polymer that is employed is somewhat limited by its necessity for having such solubility characteristics. While a precise upper limit of molecular weight is diflicult to absolutely prescribe in all instances, due to the variations in the species that may be utilized, polymers having molecular weights as high as 2000 and more may frequently be employed. Ordinarily, the phosphorous-containing polyphenolic polymer that is employed has a minimum molecular weight of about 350. Frequent-ly, it is advantageous for the phosphorous-containing polyphenolic polymers that are utilized as stabilizers in the practice of the present invention to have a molecular weight in the range from about 600 to about 1200.

As indicated, it is preferable to add a solution of the stabilizer to a polymer solution. However, complete solubility of the phosphorous-containing polyphenolic polymer stabilizer is not essential so long as it is capable of being solubilized with suitable dispersing agents, or to remain in finely divided emulsion, dispersion, or stable suspension in the solvent for the olefin polymer or in a solvent compatible and miscible with the polymer solution. The phosphorous-containing polyphenolic stabilizers are, for the most part, at least partially soluble in the common solvents for the polyolefins, as well as being soluble in lower aliphatic alcohols, i.e., methanol, ethanol, etc., ketones, aqueous sodium hydroxide or other caustic solutions.

As hereinbefore indicated, a significantly more than additive eifect of the individual effects of the phosphorouscontaining polyphenolic compound and the DLTDP or DSTDP on the level of stabilization of the olefin polymer is obtained when the two are used in combination. Thus, in some instances, particular species of the polyphenolic compounds under certain conditions may show but very little stabilizing ability, but when combined with the DLTDP or DSTDP outstanding and highly acceptable results are obtained, and conversely when DLTDP or DSTDP is used under certain conditions in the absence of the polyp'henolic compound. In all cases, the stabilizing effects of the two combined is more than additive.

The amount of the stabilizer system that is employed in the polymer compositions in accordance with the present invention is advantageously from about 0.05 to about 0.5 weight percent, based on olefin polymer weight, of the phosphorous-containing polyphenolic compound and from about 0.1 to about 0.5 weight percent, based on ole fin polymer weight of DLTDP or DSTDP. Beneficially, from between 0.1 to about 0.3 weight percent of the polyphenoic compound and from about 0.2 to about 0.4 weight percent of DLTDP or DSTDP, both based on olefin polymer weight are utilized, and, preferably, about 0.1 weight percent of the polyphenolic compound is used in combination with about 0.25 weight percent of DLTDP or DSTDP.

The olefin polymers that are treated in accordance with the invention are advantageously polymerized 2 to about 8 carbon-atom aliphatic olefins including both monoand diolefins, such as ethylene, propylene, butylene, and butadiene (including polymerizable mixtures thereof) and particularly l-olefins, which are so-designated because of their terminally unsaturated configuration.

In a preferred embodiment of the invention, the polymers stabilized according to the present teaching are the polyolefin polymers prepared by polymerization of monoolefinic aliphatic olefin monomers, such as ethylene, propylene, butylene and so forth (including polymerizatble mixtures thereof) that contain from 2 to about 8 carbon atoms. These polymers of ethylene, propylene and other non-aromatic hydrocarbon olefins may be obtained under relatively low pressures of 1 to 100 atmospheres using such catalysts for polymerizing the ethylene or other olefin as mixtures of strong reducing agents and compounds of Group IV-B, VB, and VIB metals of the Periodic System; chromium oxide on silicated alumina; hexavalent molybdenum compounds; and charcoal supported nickelcobalt. 'I'hese polymers are frequently obtained in solution by polymerizing the monoolefins in an inert solvent, preferably a hydrocarbon solvent, which may suitably be a 3 to 12 carbon atom piaraflinic or aromatic hydrocarbon solvent, such as hexane, cyclohexane, and advantageously benzene, toluene and xylene.

A particular aspect of the invention is to effectively and efficiently stabilize propylene polymers, that is, homopolymeric polypropylene [and copolymers of propylene and another 2 to 8 carbon olefin as described :hereinabove. Preferably, the propylene polymer contains at least about weight percent polymerized propylene in the polymer molecule.

The following examples are intended to further illustrate, but by no vmeans limit, the present invention, wherein unless otherwise indicated, all parts and percentages are by weight.

Example 1 A solution of propylene polymer comprising about 10 percent polymer solids in xylene was introduced into a devolatilizer feed tank. Into the same tank acetonexylene solution of the reaction product of POCl and hydr-oqui-none of mole ratio 3:7, respectively, and having an average molecular weight of about 887 and DLTDP was metered with the aid of a Lapp microfeeder pump in an amount so as to provide about 0.1 percent of the phosphorous-containing polyphenolic compound and about 0.25 percent DLTDP, based on the weight of the polymer. The tank was agitated to insure uniform stabilizer distribution. The solution was fed from the tank to the first of two shell and tube devolatilizers which operated at about 240-245 C. and atmospheric pressure. From there it was forwarded to the second stage devolatilizer which was maintained at about 245250 C. and about 1 mm. Hg vacuum. The total time the solution was in the devolatilizers was about 6 hours. Polymer was recovered The stability of the polymer was evaluated by maintaining a sample of the polymer in an air oven at 140 C. and observing the time (hours) it took for a break (darkening) in color to appear.

6. departing from the intended spirit and scope of the hereindescribed invention, which is to be interpreted by the hereto appended claims. What is claimed is:

The heat fabrication stability of the polymer, i.e., the 5 1. A stabilized olefin polymer composition comprising ability of the polymer to be fabricated wlth heat fabricaa 2 to 8 carbon-atom aliphatic olefin polymer having in- :(1011 techniques. s d rmlned 'by measuring the melt corporated therein from about 0.05 to about 0.5 weight index of the polymer before and after heating at 270 C. percent, based on olefin polymer weight, of a phosphofor 20 mmutes. The ratio of the melt ndex after heatmus-containing polyphenolic compound having the mg to the melt index before heating indicates fabrication 10 formula: stability. The lower the ratio the greater the ability of the polymer to Withstand heat fabrication without reducfll tion of molecular weight or cracking of the polymer.

The etfectiveness of the stabilizer to reduce molecular \0 weight loss of the polymer through the devolatilizers was R 11 also determined by measuring the mol la Weight f wherein Ar is a difunctional aromatic nucleus selected the polymer before (feed) and after (product) it was ffomihe g p Consisting of hydroqllinofle, P P'- P PY passed through the devolatilizers. The higher the value idene diphenoLbisphenol sulfone, bisphenol sulfoxide and of the ratio of the product molecular Weight of the feed miXtllreS thereof; each R is indepcndellfly Selectfid fffim molecular weight the less the loss in polymer molecular the group consisting of p,p-hydroxy phenyl radicals, hyweight during devolatilization. drogen, and alkali metal; and n has an average numerical The preceding procedure was followed excepting in one value from 1 to about 15; and, from about 0.1 to about case to eliminate the addition of the phosphorous-emi- 05 weight percent, based on polymer weight, of a thioditaining polyphenolic compound, in another case to elimipropionate selected from the group consisting of dilaurylnate addition of the DLTDP, and in yet another case to thiodipropionate and distearylthiodipropionate. eliminate addition of any stabilizer. 2. The olefin polymer composition of claim 1, wherein The results of the foregoing are set forth in Table 1. between about 0.1 and 0.3 weight percent of said poly- TABLE I Weight percent Polymer composition POClr-hydro- Weight percent Hours to Ratio M.W. Sample No. (wt. percent based on quinone re- DLTDP break at Fabrication product/M.W.

polymer wt.) action product (based on 140 C. stability ratio feed (based on polymer wt.) polymer wt.)

96% propylene/4% ethylene 0.1 0.25 380 1.3 ca. 0.90 Homopolypropylene 0.1 0.25 1 530 1. 3 ca. 0. 90 do 0.1 None 21 do None 0. 25 100 do None None 24 6 0.70

1 Average of three samples.

E x amp le 2 phenolic compound and between about 0.2 and about 0.4 weight percent of said thiodipropionate, both weights The procedure of Example 1 was repeated excepting to based on olefin polymer weight, are incorporated therein. substitute the reaction product of P001 and Bisphenol-A 3. The olefin polymer composition of claim 2, wherein of mole ratio 4:9, respectively, and having an average said thiodipropionate is dilaurylthiodipropionate. molecular weight of about 2212 for the PoCl -hydroqui- 4. The olefin polymer composition of claim 1, wherein none reaction product. The results are set forth in said olefin polymer is a polymer of a mono-olefinic Table II. monomer.

TABLE II Weight percent Polymer composition PoCl -bisphe- Weight percent Hours to Ratio M.W. Sample No. (wt. percent based on nol-A re- DL'IDP break at Fabrication product/MW.

polymer wt.) action product (based on 140 C. stability ratio feed (based on polymer wt.) polymer wt.)

97% propylene/3% ethylene. 0. 1 0.25 260 1. 3 ca. 0. 90 100% propylene 0. 1 0. 25 1 463 1. 3 ca. 0. 90 uo 0.1 None 21 do None 0.25 100 1 Average of three samples.

Example 3 5. The olefin polymer composition of claim 4, wherein The procedures of Examples 1-2 are repeated exceptg a piopylene p f l 5 h ing to substitute DSTDP for the DLTDP with similar 6 0 e n W F calm rw e161" excellent msulm said propylene polymer 1s polypropylene.

Similar excellent results are obtained when other of The Olefin polymer Composltlon of 31mm wherein the phosphorus-containing polyphenolic compounds and other of the olefin polymers are employed in accordance with the practice of the invention.

Other modifications and alterations will be apparent to said propylene polymer is a copolymer of propylene and ethylene.

8. The olefin polymer composition of claim 1, wherein said polyphenolic compound is a reaction product of bythose skilled in the art and can be entered into without droquinone and phosphorous oxychloride.

9. The olefin polymer composition of claim 1, Where said polyphenolic compound is a reaction product of p,p-isopropylidene diphenol and phosphorous oxychloride.

10. The method of preparing a stabilized olefin polymer which comprises admixing with a solution of a 2 to 8 carbon-atom aliphatic olefin polymer dissolved in a solvent for said polymer from about 0.05 to about 0.5 weight percent, based on olefin polymer weight, of a phosphorous-containing polyphenolic compound having the formula:

wherein Ar is a difunctional aromatic nucleus selected from the group consisting of hydroquinone, p,p-isopropylidene diphenol, bisphenol sulfone, bisphenol sulfoxide and mixtures thereof; each R is indpendently selected from the group consisting of p,p-hydroxy phenyl radicals, hydrogen, and alkali metal; and n has an average numerical value from 1 to about 15; and from about 0.1 to about 0.5 weight percent, based on polymer weight, of a thiodipropionate selected from the group consisting of dilaurylthiodipropionate and distearylthiodipropionate; heating the solution to evaporate said solvent therefrom; and subsequently recovering said polymer.

11. The method of claim 10, wherein between about 0.1 and 0.3 weight percent of said polyphenolic compound and between about 0.2 and about 0.4 weight percent of said thiodipropionate, both weights based on polymer Weight are admixed with the polymer solution.

12. The method of claim 11, wherein said thiodipropionate is dilaurylthiodipropionate.

13. The method of claim 10, wherein said olefin polymer is a polymer of a mono-olefinic monomer.

14. The method of claim 13, wherein said polymer is a propylene polymer.

15. The method of claim 14, wherein said propylene polymer is polypropylene.

16. The method of claim 14, wherein said propylene polymer is a copolymer of propylene and ethylene.

17. The method of claim 16), wherein said polyphenolic compound is a reaction product of hydroquinone and phosphorous oxychloride.

18. The method of claim 10, wherein said polyphenolic compound is a reaction product of p,p'-isopro-pylidene diphenol and phosphorous oxychloride.

19. The method of claim 10, wherein said polyphenolic compound and said thiodipropionate are dissolved in a solvent miscible with said solvent for said olefin polymer.

No references cited.

DONALD E. CZAJA, Primary Examiner.

LEON I. BERCOVITZ, Examiner. 

1. A STABILIZED OLEFIN POLYMER COMPOSITION COMPRISING A 2 TO 8 CARBON-ATOM ALIPHATIC OLEFIN POLYMER HAVING INCORPORATED THEREIN FROM ABOUT 0.05 TO ABOUT 0.5 WEIGHT PERCENT, BASED ON OLEFIN POLYMER WEIGHT, OF A PHOSPHOROUS-CONTAINING POLYPHENOLIC COMPOUND HAVING THE FORMULA: 